TabPageEnd completes a description of a page of a tab widget.

ToString converts function arguments to a json string

Widg returns a pointer to a Widget structure (a widget) with a Name member corresponding to sName argument. The sName must be compound name, containin

f(x) = x^4 - 1 z' = z - f(z)/f'(z) = z - (z^4 - 1) / (4 * z^3) = z - (z - 1/z^3) / 4